This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Prions cause transmissible, neurodegenerative diseases with invariably fatal progression. A prion is an infective particle consisting exclusively of the prion protein. Two forms are discriminated: the benign, cellular form PrPC, and the disease-causing "scrapie" isoform PrPSc, which is confirmationally rearranged. Since PrPC and PrPSc differ in structure, studies of each conformation are essential. Our apporach focuses on PrPSc. We developed a high-yield protein purification protocol. Our preparations contain prion protein 2D crystals, which are structurally analyzed with standard and low-dose cryo electron microscopy. However, to further the quality and purity of our samples, we need to identify contaminants/copurified proteins from our samples for their systematic removal. This is the task for mass spectrometry. On a collaborative basis, copurified proteins are to be identified by analysis of bands derived from Coomassie-stained polyacrylamide gels.